Pressure Volume Curve of the Respiratory System

吳健樑馬偕醫院 胸腔內科

Transmural Pressure of the Respiratory System

PA

Alveolar pressure

PIpIntraleural pressure

PTpTranspulmonary pressure

Pressure around the Balloon (Lung)

1. PTP = PA – PIP

2. PA = 0, if no air is flowi

ng into the balloon

3. PIP is subatmospheric

due to the recoil of the

lung away from the jar

4. PTP= 0 – (-10) cmH2O

= 10 cmH2O

Pressure Volume Curve of the Lung

100

75

50

25

100

0

20

40

60

80

0-20 10 20 30-10

Pressure

Volume

Vital Capacity%

TLC%

Pressure (cmH2O)

Lung recoil is due to- surface tension- elastic and collagen fibers of the lung

Resting lung

FRC

Pressure Volume Curve of the Lung

1.0

0.5

-10 -20 -30

Pressure around lung (cmH2O)

Volume (L)

Pressure Volume Curve of the Lung

1. P-V curve defines the elastic property of the lung

2. Compliance = change in volume per unit change of pressure

3. Compliance quantifies the elastic property

Calculation of Compliance

Pressure (cmH2O)

Vo

lum

e (m

l)

1.0

0.5

-10 -20 -30

Pressure around lung (cmH2O)

Volume (L)

․

․

․․

Compliance of the Lung

1. The slope is the compliance

2. The line 1 represents high compliance

3. The line 2 is low compliance

1

2

Mechanics of Chest Wall

• Chest wall = all structures surrounding the

lung that move during breathing

– i.e. rib cages, diaphragm, abdomen wall &

contents and mediastinal contents.

• Sometimes like a spring

• Sometimes like a balloon

Pressure Volume Curve of Chest Wall (I)

Pressure Volume Curve of Chest Wall (II)

100

75

50

25

100

0

20

40

60

80

0-20 10 20 30-10

Pressure

Volume

Vital Capacity%

TLC%

Pressure (cmH2O)

Resting lung

FRC

• Chest wall recoils in two directions• CW recoils outward below 75% of VC• CW recoils inward at volume > 75% of VC

Residual volume

Pressure Volume Curve of Chest Wall

Pressure

Volume

Vital Capacity%

TLC%

Pressure (cmH2O)

100

75

50

25

100

0

20

40

60

80

0-20 10 20 30-10

Resting lung

FRC

Residual volume

Pressure Volume Curve of the Respiratory System

Hysteresis of Air filled Alveolus

What Factors Contribute to Compliance

• Connective tissue of lung

• Surface tension

• Surfactant

What Factors Contribute to Compliance

• Connective tissue of lung

• Surface tension

• Surfactant

Surface TensionThe weight in the bubble is the collapsing pressure of the bubble

Law of Laplace (inward pressure of bubble):P =2 T/r (T:surface tension; r: radius)

MV

SurfactantSurfactant is produced by type II alveolar cell. The type II cells have characteristic microvilli (MV).

Functions of Surfactant

• Surfactant is a DPPC (DiPalmitoyl Phosphatidyl Choline) protein with a hydrophobic at one end and hydrophilic at the other.

• Reduce surface tension by intermolecular repulsive force

Repulsive Force of Surfactant Molecule

SurfactantDepletedlung

Influence of Surfactant on PV Curve of Lung

What Does Compliance Mean

• Compliance– easier to in/deflate– steep curve: less pressure needed for

unit volume change

• Compliance – difficult to in/deflate– flat curve

Commonly Used Methods for Measuring PV Curve

• Supersyringe method

• Flow interrupter

• Low-flow method

The supersyringe techniqueDisconnection

Time consuming

Volume loss

P-V curveMethodology

The supersyringe technique

P-V curveMethodology

The multiple occlusion technique

Complexity

Volume history

Recorded in 8.38 +/- 1.19 min…

Servillo, 2000

P-V curveMethodology

Quin Lu, 1999

The low flow technique

Popular (many validation studies)

The Pres should be known

And substracted…

Not usable in case of leak

Pmax should be adjusted

No way for the deflation

P-V curveMethodology

Comparison of PV curves by Different Methods(Qin et al ARRCCM 1999)

Compliance (mL/cmH20): Volume/ pressure

Why it is important?1. Physiology: how much work to produce a volume.

2. Prognosis: Low/high CRS = poor prognosis

3. Treatments: PEEP/VT/recruitment maneuvers

Why is it complex?1. One point is not enough…

2. Affected by chest wall, abdomen, tube resistances…

3. Dynamic versus quasi-static…

4. Inflation or deflation curve…

Clinical Uses of P-V Curve

1. Allow initial estimate of lung pathology2. Presence of lower inflection point suggePresence of lower inflection point sugge

sts compression atelectasis rather than sts compression atelectasis rather than consolidationconsolidation

3. Recruitment proportional to the applied Recruitment proportional to the applied PEEP linear P-V curvePEEP linear P-V curve

4. An inflection point of the chest wall may An inflection point of the chest wall may lead to erroneous interpretation of PV culead to erroneous interpretation of PV curve of respiratory system.rve of respiratory system.　　

Normal

Restrictive(ARDS)

Obstructive(COPD)

P-V curveThe “Classical” Approach

P-V Curves in Different Stages of ARDS

Airway Pressure, cmH2O

Vol

ume

(%)

20

80

60

100

40

3015 20 25105 35 40

Recovery stageEarly stageIntermediate stageFibrotic stage

Clinical Uses of P-V Curve

1. Allow initial estimate of lung pathologyAllow initial estimate of lung pathology2. Presence of lower inflection point indicat

es the opening pressure of the atelectatic alveoli

3. Recruitment proportional to the applied Recruitment proportional to the applied PEEP linear P-V curvePEEP linear P-V curve

4. An inflection point of the chest wall may An inflection point of the chest wall may lead to erroneous interpretation of PV culead to erroneous interpretation of PV curve of respiratory system.rve of respiratory system.　

Nonrecruitable

AtelectaticRecruitable

Normal

Pathophysiology

Acute Respiratory Distress Syndrome

Non-recruitable

AtelectaticRecruitable

Normal

Acute Respiratory Distress Syndrome

Effects of PEEP

PEEP

M. Tobin, NEJM 2001

P-V curve

Compliance (mL/cmH20): Volume/ pressure

The 3 segmental analysis of the Venegas (JAP, 1998) model

Best compliance

Over

distention of

lung units

Collapse of

peripheral

airways and

lung units

Ventral

Dorsal

Gas-Tissue Ratio Distribution in Lung Region

Gattinoni et al. JAMA 1993;269:2122

Gattinoni L, AJRCCM 2001

P-V curveThe “Modern” Approach

The sponge model and the superimposed pressure (SP)…

gas tissue

0

0.2

0.6

0.4

‧ ‧ ‧ ‧ ‧ ‧ ‧‧ ‧‧‧

●●0

0.2

0.6

0.4

● ● ● ● ● ●●

●

●

●●

0

0.2

0.6

0.4● ●

●● ●

● ●● ●

0 204 8 12 16

Gas

/Tis

sue

Rat

i on

Gas

/Tis

sue

Rat

i on

Gas

/Tis

sue

Rat

i on

PEEP, cmH2O

Gas/Tissue Ratio as A Function of PEEP

Gattinoni et al. JAMA

Pflex

Clinical Uses of P-V Curve

1. Allow initial estimate of lung pathologyAllow initial estimate of lung pathology2. Presence of lower inflection point indicatPresence of lower inflection point indicat

es the opening pressure of the atelectaties the opening pressure of the atelectatic alveolic alveoli

3. Recruitment proportional to the applied PEEP linear P-V curve

4. An inflection point of the chest wall may An inflection point of the chest wall may lead to erroneous interpretation of PV culead to erroneous interpretation of PV curve of respiratory system.rve of respiratory system.　

P-V curveThe “Modern” Approach

SP0 SP5 SP10SP15

P-V curveThe “Modern” Approach

UIP = end of recruitment

LIP = start of recruitment

Recruitment zone

CT findings of Lung recruitment during Inspiration

Pressure – Volume Curves in ARDS caused by Pulmonary and Extrapulmonary disease

P-V curveThe “Modern” Approach

Peter C. Rimensberger

CRITICAL CARE MEDICINE 1999;27:1946-1952

Maggiore, AJRCCM 2001

P-V curveThe “Modern” Approach

De-recruitment even at high PEEP.

No correlation between VDER and the LIP.

The steeper the curve in ZEEP (potential for recruitment) and the highest the volume recruited by PEEP

Clinical Uses of P-V Curve

1. Allow initial estimate of lung pathologyAllow initial estimate of lung pathology2. Presence of lower inflection point indicatPresence of lower inflection point indicat

es the opening pressure of the atelectaties the opening pressure of the atelectatic alveolic alveoli

3. Recruitment proportional to the applied Recruitment proportional to the applied PEEP linear P-V curvePEEP linear P-V curve

4. An inflection point of the chest wall may lead to erroneous interpretation of PV curve of respiratory system.　

V

Pst,rs

V

Pst,cw Pst,L

Surgical ARDS

Medical ARDS

UIP(VT =0.5)UIP(VT =0.7)

LIP =18 LIP =16

Impaired Lung and Chest wall mechanics in PV curves in ARDS

Ranieri et al AJRCCM 1997

The P-V curveConclusions

Understanding the PV curve:

The LIP: start of recruitment

The UIP: end of recruitment

Middle part: recruitment zone

Methodology:

Inflation and deflation

Pressure ramp method (?)

Clinical implications:

Recruitment maneuver

Optimum PEEPMaximum volume at equivalent pressure

Minimal hysteresis

Minimum slope

Adjust PEEP Level Based on Pflex

UIP

LIP

P-V loops on monitoring screen of MV

Plot of P-V loop from scalars of pressure and volume

P-V Loop: different resistance

C1 C2 C3

P-V loops: change in compliances

P-V loops: change in resistance

Work of Breathing

Esophageal Balloon

• The balloon should be 5 -10 cm long and 3.2 – 4.8 cm perimeter• The volume is 0.5 ml

LatexBalloon

Position of Esophageal Balloon

Methods of Confirmation of Optimal Balloon Placement

1. Dynamic occlusion test

– Compare the change in Pm and Pes during serial inspiratory efforts against occluded airway

2. Stomach placement

– Insert catheter into stomach first, then pull back into esophagus until negative pressure waveform

Pm (cmH2O)

Pes

(cm

H2O

)

0

10

5

50 10

Tracing of Volume, Pes and Pm during a dynamic occlusion test

Clinical Uses of Esophageal Pressure Measurement

• To determine the presence of dynamic intrinsic PEEP

• To assess the lung mechanics and respiratory mechanics (work of breathing)

• To interpret pulmonary properly vascular pressures during hemodynamic monitoring

Determination of Dynamic PEEPi using Esophageal Pressure

Pressure Waveform Indicating The Presence of auto-PEEP

Different Static and Dynamic auto-PEEP

-4 0

Esophageal pressure (cmH2O)

Ccw

-5

200

-2

400

600

Esophageal pressure (cmH2O)

Vo

lum

e (m

l)

Plots of Esophageal pressure vs volume during Unassisted and Passive br

eathing

CL,dyn

-5

200

0

400

600

Esophageal pressure (cmH2O)

Vol

ume

(ml)

Esophageal pressure vs volume during unassisted ventilation

Elastic work

Resistive work

CL,dyn Ccw

Influence of Pleural Pressure on Hemodynamic Monitoring

5 15 15-5 -5 15

LALA LA

HighPleural

Pressure

Normal LowMyocardialCompliance

Ppl = PEEP x {CL/ CL + CCW}